In teleconferencing, conference participants are brought together via a communication link for the purpose of information exchange. The "tele" prefix to the word telecommunications implies that one or more of the participants is remotely located from the other participants in the conference. Teleconferencing is a function which has been performed using prior art techniques and apparatus to give the perception that there is no distance barrier between participants who may actually be widely separated.
In view of the inherent limitations of audio teleconferencing, there developed numerous prior art methods and apparatus to add a video dimension to the teleconferencing function. However, each of these approaches has provided for the centralized control of respective video cameras or has placed control in the hands of the calling party alone.
In the former approach, all of the intelligence in a video teleconferencing system was placed in a central facility or central computing area in close proximity to the subscribers and control signals were distributed over thick cables to each of the stations. In view of the nature of these signals, low voltage A/C and D/C power, the length of the cables was limited to a few hundred feet. These prior art systems required individual wires between each of the cameras and a centralized switch for every camera control function (right, left, up, down, focus, zoom and iris). For short runs and few cameras, this was a reasonable solution, but for many cameras and longer runs, the cost for cable and installation became unreasonable. Moreover, subscriber stations which were not located within the distance limits imposed by the factors above, could not be included in a video teleconferencing scheme.
In the latter design, centralized control was placed in the hands of a conference leader who could effect the functions necessary to carry on a teleconferencing scenario and select locally generated images for transmission to a remote site so as to give the remote participants the perception of no distance barrier between themselves and other remotely located sites. However, in this latter design, the picture view was dependent upon the skill and operation of the conference leader. Remote subscribers had no control over the view that they received.
For a review of past approaches to video teleconferencing, see "THE GLOBAL VIDEO CONFERENCE" by Mokhoff appearing in IEEE Spectrum, September, 1980, pp. 44-47. See also, U.S. Pat. No. 4,516,156 issued to Fabris et al. on May 7, 1985 entitled "TELECONFERENCING METHOD AND SYSTEM"; U.S. Pat. No. 3,636,265 issued to Kikuchi et al. on Jan. 18, 1972 entitled "TELEVISION CONFERENCE TELEPHONE SYSTEM"; and U.S. Pat. No. 4,264,928 issued to Schober on Apr. 28, 1981 entitled "CONFERENCE VIDEO SYSTEM".
U.S. Pat. No. 4,516,156 issued to Fabris discloses a video teleconferencing method and system which is adapted to be connected by a wide band digital communication link, such as a domestic satellite communication system or a microwave communication system and further including at least a pair of teleconferencing sites, remotely located from each other. According to
Fabris, each of the teleconferencing sites further includes at least a pair of TV cameras, readily controllable by the conference leader in terms of pan, tilt, zoom and focus, so that a video image can be transmitted from one site to another. Fabris further discloses the use of at least a pair of video displays under the control of the conference leader, allowing the conference leader to select the image that will be portrayed on each display from at least among a remotely generated video image and a locally-generated video image.
U.S. Pat. No. 3,636,265 issued to Kakuchi et al., discloses a television conference telephone system comprising a plurality of terminal equipments adapted to transmit and receive audio signals and video signals, means to connect to the conference telephone system terminal equipments of subscribers attending the conference, selector means corresponding to said plurality of terminal equipments, control logic means operating only the selector means corresponding to the terminal equipment of a particular subscriber attending the conference, and a video signal distributing means which is responsive to the selector means to supply the video signal of only a particular subscriber to television receivers of terminal equipments of all subscribers attending the conference. Kakuchi's system further provides for the ability of a talking subscriber or attendant to monitor its own condition and ascertain whether the presented charts or data and the like are properly displayed and transmitted.
U.S. Pat. No. 4,264,928 issued to Schober discloses a conference video system including a plurality of conference seats and microphones, a TV camera and a pivotable mirror which directs light from the conference seats to the TV camera. As disclosed by Schober, each of the microphones is coupled through circuit elements to a servomotor(s) which positions the mirror to focus on the speaker and aims the camera's field of vision toward active audio. The electronic portion of the system utilizes the time, two adjacent microphones receive a speaker's voice to generate a signal used to drive the servomotor to perform its mirror-positioning function.